Conventionally, a medium processing apparatus provided with a printing function in which printing of a character is performed on a card in a thermal method has been known (see, for example, Patent Literature 1). The medium processing apparatus described in Patent Literature 1 includes a printing unit having a thermal head, which is structured to be abutted with a card to perform printing on a card, and a platen roller which is oppositely disposed to the thermal head. The printing unit includes, in addition to the thermal head, a solenoid which moves the thermal head in a direction where the thermal head is abutted with the platen roller and in a direction where the thermal head is separated from the platen roller, a support part which supports the thermal head, and a tension coil spring for urging the thermal head toward the platen roller. The support part includes a drive source fixing member to which the solenoid is fixed and a head fixing member to which the thermal head is fixed. The head fixing member is held by the drive source fixing member so as to be capable of turning with a turning center shaft attached to the drive source fixing member as a turning center.
In the medium processing apparatus, one end side of each of tension coil springs is engaged with each of both side faces of the head fixing member in a card widthwise direction. The other end side of each of the tension coil springs is attached to a main body of the medium processing apparatus and the head fixing member is urged toward the platen roller by the urging forces of the tension coil springs. Further, the head fixing member is formed with a shaft engaging groove with which the turning center shaft is engaged and the shaft engaging groove is formed in a “U”-groove shape which is a substantially “U” shape when viewed in a card widthwise direction. Therefore, in the medium processing apparatus, even when a card with which the thermal head is abutted is deformed, the thermal head is inclined together with the head fixing member and thereby the thermal head is capable of following the deformed card.